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The Morphology and Surface Features of Olivine in Kimberlite Lava: Implications for Ascent and Emplacement Mechanisms : Volume 5, Issue 2 (13/12/2013)

By Jones, T. J.

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Book Id: WPLBN0004021900
Format Type: PDF Article :
File Size: Pages 30
Reproduction Date: 2015

Title: The Morphology and Surface Features of Olivine in Kimberlite Lava: Implications for Ascent and Emplacement Mechanisms : Volume 5, Issue 2 (13/12/2013)  
Author: Jones, T. J.
Volume: Vol. 5, Issue 2
Language: English
Subject: Science, Solid, Earth
Collections: Periodicals: Journal and Magazine Collection, Copernicus GmbH
Historic
Publication Date:
2013
Publisher: Copernicus Gmbh, Göttingen, Germany
Member Page: Copernicus Publications

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Porritt, L. A., Russell, J. K., Brown, R. J., & Jones, T. J. (2013). The Morphology and Surface Features of Olivine in Kimberlite Lava: Implications for Ascent and Emplacement Mechanisms : Volume 5, Issue 2 (13/12/2013). Retrieved from http://worldlibrary.in/


Description
Description: Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, V6T 1 Z4, Canada. Many kimberlite rocks contain large proportions of ellipsoidal-shaped xenocrystic olivine grains that are derived mainly from the disaggregation of peridotite. Xenocrystic olivine grains from a lava erupted from the Quaternary Igwisi Hills kimberlites, Tanzania, are compared to phenocrystic olivine, liberated from picritic lavas, and mantle olivine, liberated from a fresh peridotite xenolith, in order to examine the potential modification of olivine surface textures due to transport from the mantle to the surface within kimberlite magmas. Image analysis, SEM imagery and laser microscopy reveals significant differences in the surface features and morphologies of the three crystal populations. Xenocrystic olivine grains are characterised by rough surfaces, ellipsoidal shapes and impact pits. Mantle olivines are characterised by flaked surfaces and indented shapes consistent with growth as a crystal aggregates. Phenocrystic olivines are smooth-surfaced and exhibit flat crystal faces. We infer that the distinctive shapes and surfaces of xenocrystic olivine grains resulted from three distinct mechanical processes attending their rapid transport from their source in the mantle lithosphere: (1) penetrative flaking from micro-tensile failure induced by rapid decompression; (2) sustained abrasion and attrition arising from particle-particle collisions between grains in a turbulent, volatile-rich flow regime, and; (3) higher energy particle-particle collisions that produced impact cavities superimposed on decompression structures. The combination of these processes during the rapid ascent of kimberlite magmas is responsible for the distinctive ellipsoidal shape of olivine xenocrysts found in kimberlites worldwide.

Summary
The morphology and surface features of olivine in kimberlite lava: implications for ascent and emplacement mechanisms

Excerpt
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